Process for starting a continuous casting mold

ABSTRACT

A method of initiating a continuous casting mold includes steps of positioning a plug inside a continuous casting mold, sealing the plug with respect to inner walls of the mold, positioning a prefabricated chill member on a top surface of the plug; and introducing molten metal into the mold. By prefabricating the chill member, valuable time is saved during the mold startup phase. The prefabricated chill member may have a compressible metallic sealing strip secured thereto to enhance sealing against the mold wall without abrading or scratching the mold wall. Another aspect of the invention involves sealing the gaps that exist between the mold surfaces and the mold plug by use of a an elongated body that defines in cross-section a broadened upper portion and a tapered lower portion that narrows into a leading edge. This construction permits the sealing element to be quickly inserted into a gap without being caught on the mold plug.

[0001] This is a continuation of application Ser. No. 09/321,245, filedMay 27, 1999, the entire disclosure of which is hereby incorporated asif set forth fully herein.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates generally to the field of continuouscasting of metals, and more specifically processes and equipment thatare used to initiate casting in a continuous casting mold.

[0004] 2. Description of the Related Technology

[0005] In the conventional continuous casting process, molten metal ispoured into an open top of a mold that also has an open bottom. As itcools, the metal solidifies against water-chilled interior walls of themold to form a solidified skin surrounding a molten core. Thesolidifying strand emerges from the lower end of the mold and is guidedaway from the mold. After the strand leaves the mold, cooling continuesby the use of water sprays so that the core ultimately solidifies. Theconventional process involves withdrawing the partially solidifiedstrand downwardly, and gradually curving the strand along an arc untilit continues in a horizontal direction for cutting. The movement of thestrand along the arc involves guiding the strand with appropriate guiderollers. Then, the strand is cut to desired lengths for furtherprocessing.

[0006] Before the casting operation can be initiated, the lower end ofthe mold must be temporarily plugged to prevent the molten metal fromsimply running through it. In other words, the molten metal must beretained within the mold for a sufficient period of time forsolidification to begin. Conventionally, the plug or “dummy bar head” isheld in place by a what is commonly termed a “dummy bar,” or “starterbar,” which is an elongated strip or chain having an end fastened to themold plug.

[0007] After solidification occurs near the bottom of the mold, theincipient strand will itself plug the bottom of the mold, so the starterplug is no longer necessary. An endwise pulling force on the dummy barwithdraws the plug from the mold and draws the plug and attached strandalong the arcuate path that is defined by the guide rollers. The strandis eventually separated from the dummy bar so that the dummy bar can bereused.

[0008] When the plug is placed in the mold, clearance is provided for sothat the plug may be safely inserted without damaging the mold's innersurfaces, thus a gap exists around the perimeter of the plug. However,it is essential that the plug form a tight seal with the walls of themold. Molten steel has a viscosity approximating that of water, and canquickly leak from the mold if the plug is not well seated. In the past,asbestos cord was used as packing about the plug to ensure a tight seal.For environmental reasons, however, asbestos is no longer used and hasbeen replaced with alternative materials such as board that isfabricated from heat-resistant ceramic material such as vitreousaluminosilicate fibers.

[0009]FIG. 1 is a diagrammatic depiction of a continuous casting machine10, which, as is conventional, has mold walls 12 with inner mold wallsurfaces 14. A dummy bar 16 is shown positioned in the mold 10 and amold plug 18 is secured to the dummy bar 16. Currently, after the plughas been placed in the mold, strips 20 of the fibrous material arepushed downwardly from the top of the mold into the gaps between theplug and the mold walls. The fibrous material, as is shown incross-section in FIG. 2, is tapered, but has a flat leading surface 21that can become jammed against the plug 18 during insertion.

[0010] As is shown in FIG. 2, in order to accelerate solidification ofthe molten metal against the plug 18 during the startup phase, it iscommon to position pieces of metal scrap or metal shavings on the topsurface of the plug 18, particularly near the mold side walls 14. Thisso-called “chill scrap” effectively absorbs heat energy from the moltenmetal, hastening the liquid to solid phase change of the molten metal.Typically, fine chill material 21 such as nail whiskers is first pouredon top of the plug, particularly near the mold walls and on top of thefibrous sealing material, which would otherwise be quickly burnedthrough by the molten metal were it allowed to come into direct contactwith the molten metal. After this has been done, larger pieces 22 ofchill scrap material are added to enhance the cooling effect.

[0011] In any continuous casting machine, it is advantageous to be ableto perform the startup phase as quickly and as efficiently as possible.This is especially so in the case of a dual or twin strand machine,which includes two separate molds that are serviced by a common tundish.In such machines, it is deemed by some steel producers to be too riskyfor reasons of safety to perform the startup phase for one mold whilethe other mold is in operation and the tundish remains positionedoverhead. Consequently, either the active mold must be shut down, whichwould be prohibitively expensive, or the startup phase for the inactivemold must be performed in the limited period of time that exists duringa tundish change, which can be as little as two minutes. It is verydifficult to position the dummy bar, install the starter plug, positionthe chill scrap and seal the gaps between the plug and the mold walls inthis short period of time.

[0012] A need exists for an improved process of plugging and sealing acontinuous casting mold during the startup phase that is faster and moreefficient than the processes that are in conventional use.

SUMMARY OF THE INVENTION

[0013] Accordingly, it is an object of the invention to provide animproved process of plugging, sealing, and inserting chill scrap into acontinuous casting mold for the startup of a casting strand that isfaster and more efficient than the processes that are in conventionaluse.

[0014] In order to achieve the above and other objects of the invention,a method of initiating a continuous casting mold includes, according toa first aspect of the invention, steps of positioning a plug inside acontinuous casting mold; sealing the plug with respect to inner walls ofthe continuous casting mold; positioning a prefabricated chill member ona top surface of the plug; and introducing molten metal into the mold,whereby the continuous casting process is initiated quickly andefficiently.

[0015] According to a second aspect of the invention, a method ofinitiating a continuous casting mold includes steps of positioning aplug inside a continuous casting mold; sealing the plug with respect toinner walls of the continuous casting mold by a process comprisinginserting a leading edge of a sealing element downwardly into a gapbetween the plug and an inner wall of the continuous casting mold; andintroducing molten metal into the mold, whereby the continuous castingprocess is initiated quickly and efficiently.

[0016] According to a third aspect of the invention, a prefabricatedchill member for use inside a continuous casting mold during a startupphase, includes a plurality of metallic scraps that are fastenedtogether into an integral member, the member being shaped so as toapproximate a shape of a portion of an inner wall of a continuouscasting mold, whereby when the member is positioned within the mold on amold plug it will provide cooling to molten metal that is inserted intothe mold during a startup phase of continuous casting mold, thusaccelerating solidification of the molten metal in the area of the plug.

[0017] According to a fourth aspect of the invention, a sealing elementfor sealing a gap between a mold plug and an inner wall of a continuouscasting mold during the startup phase of a continuous casting machine,includes an elongated body that defines in cross-section a broadenedupper portion, and a tapered lower portion that narrows into a leadingedge, whereby the sealing element can be quickly inserted into a gapwithout being caught on the mold plug.

[0018] These and various other advantages and features of novelty thatcharacterize the invention are pointed out with particularity in theclaims annexed hereto and forming a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to the accompanying descriptive matter, inwhich there is illustrated and described a preferred embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a diagrammatical depiction of a first step of aconventional process of preparing a continuous casting mold foroperation;

[0020]FIG. 2 is a diagrammatical depiction of a second step of aconventional process of preparing a continuous casting mold foroperation;

[0021]FIG. 3 is a diagrammatical depiction of a first step of a processof preparing a continuous casting mold for operation according to apreferred embodiment of the invention;

[0022]FIG. 4 is a diagrammatical depiction of a second step of a processof preparing a continuous casting mold for operation according to apreferred embodiment of the invention;

[0023]FIG. 5 is a diagrammatical depiction of a third step of a processof preparing a continuous casting mold for operation according to apreferred embodiment of the invention;

[0024]FIG. 6 is a diagrammatical depiction of a prefabricated chillmember constructed according to another embodiment of the invention; and

[0025]FIGS. 7 and 8 are diagrammatical depictions of a prefabricatedchill member constructed according to yet another embodiment of theinvention, showing the member is uncompressed and compressed states,respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0026] Referring now to the drawings, wherein like reference numeralsdesignate corresponding structure throughout the views, and referring inparticular to FIG. 3, a continuous casting mold 10 is diagrammaticallydepicted which includes a plurality of mold walls 12, each having aninside surface 14. As may be seen in FIG. 3, the dummy bar 16 ispositioned within the continuous casting mold 10 and includes a moldplug 18 that is shaped so as to generally conform to the space that isdefined by the inner surfaces 14 of the mold walls 12. However, as isdescribed above, gaps exist between the mold plug 18 and the innersurfaces 14 of the mold walls 12.

[0027] According to one important aspect of the invention, sealing iseffected between mold plug 18 and the inner surfaces 14 by inserting atleast one sealing element 24, which is shaped as an elongated body thatdefines in cross section a broadened upper portion and a tapered lowerportion that narrows into a leading edge 25, so that the sealingelements 24 can be quickly inserted into the gaps without being caughton the mold plug 18. As is evident from the drawings and the descriptionprovided above, the insertion of the sealing elements 24 is performed insitu, or in other words the sealing elements are inserted into the gapsbetween the mold plug 18 and the mold wall 12 after the mold plug hasalready been inserted into the continuous casting mold. The sealingelement is also modified or manufactured to fit perfectly in the gapbetween the mold walls and plug to enhance quick insertion. This insuresthat valuable time will not be wasted when positioning the sealingelements. Preferably, the sealing elements 24 are fabricated fromheat-resistant ceramic material such as vitreous aluminosilicate fibers,which are readily commercially available. Alternatively, sealingelements may be used that are fabricated from a wire mesh rope.

[0028] Turning now to FIG. 4, another important aspect of the inventioninvolves the use of a prefabricated chill member 26 that is preparedprior to being placed within the continuous casting mold. Preferably,the prefabricated chill member 26 is formed in a predetermined shape soas to include at least one portion that is substantially complementaryto one of the inner surfaces 14 of the mold wall 12. Most preferably, asmay be seen in FIG. 4, the fabricated chill member 26 is shaped so as tosubstantially conform to the top of mold plug 18 and to the boundariesof the space that is defined by the inner surfaces 14 of the mold walls12. Preferably, prefabricated chill member 26 is fabricated from aplurality of metal scraps that are welded together, although alternativematerials and alternative fabrication techniques could also be usedwithin the spirit of the invention. The prefabricated chill member isalso manufactured to completely cover the sealing material to reduce thechance of steel leakage.

[0029] As may be seen in FIG. 5, after the prefabricated chill member 26is placed in position, molten metal 30 is introduced into the continuouscasting mold 10. In one embodiment of the invention, fine chill scrapmaterial may be placed on top of the prefabricated chill member 26,particularly around the outer edges, prior to introducing the moltenmetal. The presence of the prefabricated chill member 26 will helpquickly conduct heat away from the portion of the molten metal 30 thatis adjacent to the plug 18, thus accelerating the phase change of themolten metal 30 from a liquid to a solid. It also acts to prevent themolten metal from sticking to the plug. During this time, the moltenmetal 30 is prevented from leaking out of the continuous casting mold 10by the presence of the sealing element or elements 24. As the incipientcasting 28 continues to form, the dummy bar 16 and plug 18 are pulledfrom the bottom of the continuous casting mold 10, thus initiating thecontinuous casting process.

[0030]FIG. 6 depicts another embodiment of the invention, wherein,instead of the sealing elements 24, a compressible sealing strip 32 ispre-attached to the prefabricated chill member 26 prior to the insertionof the chill member 26 into the mold. In the embodiment of FIG. 6, thecompressible sealing strip 32 is generally V-shaped, and is fabricatedfrom a resilient metallic material, such as a spring steel.

[0031] The compressibility of the sealing strip 32 is beneficial becausethe walls of a continuous casting mold are tapered, and it is importantthat the mold plug both effectively seal against the mold walls and notscratch or abrade the mold walls when it is inserted into or withdrawnfrom the mold. It will be apparent from FIG. 6 that when theprefabricated chill member 26 is inserted from above into the mold thatthe strip 32 will deflect inwardly when it contacts the mold wall, thusforming a tight seal with the mold wall without scratching it. Finechill material such as nail whiskers 21 may be poured in from aboveafter the mold plug and dummy bar have been positioned, thus filling thearea above the sealing strip 32 and protecting the sealing strip 32 frombum-through when the molten metal is introduced.

[0032]FIGS. 7 and 8 are diagrammatical depictions of a prefabricatedchill member constructed according to yet another embodiment of theinvention, showing the member in uncompressed and compressed states,respectively. Specifically, FIGS. 7 and 8 depict a modification of theembodiment of FIG. 6 wherein the interior area of the V-shaped sealingstrip 32 is pre-filled with a compressible foam or filler material 34,such as expandable low density polystyrene foam, which will remainflexible after introduction and maintain the flexibility of the sealingstrip 32 during the mold start-up phase. The filler material 34 wouldalso act as a barrier between the mold wall and the fine chill material21 after the fine chill material 21 is introduced to further reduce thepossibility of mold wall scratching or abrasion.

[0033] Through use of the invention as described herein, the operator ofa continuous casting machine will be able to re-start a down strandquickly, such as during the short interruption of casting that occursduring a tundish change.

[0034] It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

What is claimed is:
 1. A method of initiating a continuous casting mold,comprising steps of: (a) positioning a plug inside a continuous castingmold; (b) sealing the plug with respect to inner walls of the continuouscasting mold by a process comprising inserting, in situ within the mold,a leading edge of a sealing element downwardly into a gap between theplug and an inner wall of the continuous casting mold; (c) positioning aprefabricated chill member on a top surface of the plug; and (d)introducing molten metal into the mold, whereby the continuous castingprocess is initiated quickly and efficiently.
 2. A method according toclaim 1, further comprising a step, performed prior to step (a), offabricating said chill member into a predetermined shape out of metalliccomponents.
 3. A method according to claim 2, wherein said step offabricating said chill member into a predetermined shape out of metalliccomponents comprises fabricating said chill member out of metal scrap.4. A method according to claim 2, wherein said predetermined shapeincludes portions that are shaped so a to be substantially complementaryto the outer portion of a dummy bar head.
 5. A method according to claim2, wherein said predetermined shape includes portions that are shaped soa to be substantially complementary to the inner walls of the continuouscasting mold.
 6. A method according to claim 2, wherein saidprefabricated chill member comprises at least one compressible metallicsealing strip on an edge thereof, and wherein step (c) comprisescompressively engaging a mold wall with the sealing strip.
 7. A methodaccording to claim 6, wherein said sealing strip is generally V-shaped.8. A method according to claim 7, further comprising a step ofpre-filling said V-shaped sealing strip with a compressible non-metallicmaterial.
 9. A method according to claim 1, wherein step (b) comprisesinserting a leading edge of a sealing element downwardly into a gapbetween the plug and an inner wall of the continuous casting mold.
 10. Amethod of initiating a continuous casting mold, comprising steps of: (a)positioning a plug inside a continuous casting mold; (b) sealing theplug with respect to inner walls of the continuous casting mold by aprocess comprising inserting, in situ within the mold, a leading edge ofa sealing element downwardly into a gap between the plug and an innerwall of the continuous casting mold; and (c) introducing molten metalinto the mold, whereby the continuous casting process is initiatedquickly and efficiently.
 11. A method according to claim 10, whereinstep (b) is performed with a sealing element that is fabricated from amaterial comprising board that is fabricated from heat-resistant ceramicmaterial.